purr like a cat

purr like a cat

1. Of an engine, motor, or other piece of machinery, to run very smoothly and efficiently (often signified by a smooth, rich humming noise, not unlike that of a cat's purr). Once get this carburetor repaired, this old car is going to purr like a cat again. I just replaced the motherboard on my PC and installed a bunch of new RAM—now it's purring like a cat.
2. Of person, to sigh, hum, or moan with contentment or pleasure. The kids purred like cats as they ate their ice cream cones. I know a few tricks that will have your partner purring like a cat.
See also: cat, like, purr
Farlex Dictionary of Idioms.

purr like a cat

 and purr like a kitten 
1. Fig. [for an engine] to run well and smoothly. My car really purred after I got it tuned up. New sparkplugs and this old heap will really purr like a cat.
2. Fig. [for a person] to be very pleased, and perhaps moan or purr with pleasure. She was so pleased that she purred like a cat. Sarah really purrs like a kitten when she is happy.
See also: cat, like, purr
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

purr (like a cat)

in. [for an engine] to run well and smoothly. New spark plugs and this old heap will really purr like a cat.
See also: cat, like, purr
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • pur
  • purr
  • purr like a kitten
  • hit on all six
  • start up
  • repair to
  • repair to (some place)
  • repair to some place
  • be in a groove
  • groove